Preparation And Electrochemical Performance Study Of Co、Ni、Mn Based Electrode For Supercapacitor

Supercapacitors,important electrochemical energy storage devices,have attracted a great deal of attention owing to their unique advantages of fast charging/discharging ability,long cycle life,and high power density.Although supercapacitors have a high power density,they usually suffer from a lower energy density than rechargeable batteries.Advanced supercapacitors must be developed with higher operating voltage and higher energy without sacrificing the power delivery and cycle life to meet the energy demands for practical applications in the future.Meanwhile,the wearable and portable electronic devices,such as bendable smart phones,electronic skins and implantable medical devices,are attracting extensive attention because of good flexibility,mechanical durability,lightweight and high portability.In order to ensure the good operation of these devices in practical applications,it is important to develop flexible energy storage technologies with high performance and long-term durability even at serious deformation conditions.Therefore,in this study,we have prepared some supercapacitors with high performance,high voltage and high flexibility,which are expected to be used in the future energy storage field.We prepared a novel design of an ASC based on NiO nanosheets composite as the positive electrode and a-Fe2O3 as the negative electrode.Our optimal ASC shows a maximum energy density of 12.4 W h kg-1 with good cycle performance(85%capacitance after 10,000 cycles).This unique design has the following merits.First,both the negative material and the positive electrode are good pseudocapacitive metal oxides.They are an attractive candidate for high-performance supercapacitors because of its low cost,high theoretical capacitance,ready availability,environmentally benign nature,and good stability in alkaline electrolytes.In the study,there is few reports focus on new ASC system based on NiO and α-Fe2O3.Second,as an efficient energy storage devices,the ASC could actuate electronic products through charged/discharge process.The as-fabricated ASC with three components connected in series can easily lightened the blue LEDs which demonstrated.Therefore,solid-state SCs hold many advantages such as environmental friendliness,portability and avoid electrolyte leakage.We present a novel route to fabricate FSCs based on a high-performance flexible fiber electrode and hybrid film electrode.Very cheap polyester fiber was selected as the fiber substrate to form the fiber electrodes.Large scale NiCo2O4 nanosheets assembled by numerous nanosheets were synthesized on a fiber substrate through a facile hydrothermal method.The free-standing NiCo2O4/polyester fiber nanosheet(NPNs)electrode exhibits ultrahigh flexibility,toughness,and electrochemical performance.Moreover,the self-supported hybrid carbon nanotube(CNT)/molybdenum oxide(MoO3)films electrode(CMF)was also prepared via a simple and rapid vacuum filtration method.The combination of MoO3 nanobelts and CNTs can enhance the electrochemical activity of MoO3 due to the high conductivity of carbon nanotubes via quickly collecting and moving charges back and forth from MoO3.Then,the one-dimensional nanobelts are interpenetrated between adjacent CNTs to avoid their overlapping and gathering and to yield an enlarged electrode/electrolyte interface area for the supercapacitor.The nanostructure can also shorten the electronic transmission path to improve the reaction kinetics.In addition to the abovementioned main advantages,this combination can not only be directly used as film electrodes and work under high bending states,but also match the fiber electrode for the assembly of a miniature fibrous device.Finally,the NiCo2O4/polyester fiber//CNT/MoO3(NPNs//CMF)was successfully prepared as a new-fashioned device to store energy.The NPNs//CMF fiber supercapacitor demonstrates a high volumetric capacitance up to 28.8 F cm-3 at 0.17 A cm-3,which corresponds to an ultrahigh energy density of 7.9 mW h cm-3.After 10 000 cycles,the volumetric capacitance can remain 98.6%.We introduce a high-performance multi-functional solid-state symmetric supercapacitor(SC)based on nano structured δ-Mno2@CNTs@sponge electrodes(MCS).The MCS was prepared by a simple“dipping and drying" and chemical bath method.The as-prepared freestanding MCS is lightweight,compressible and bendable.The MCS shows ultra-high volume recovery degree(94.5%)in the case of 80%compression.The prepared compressible MCS-SSCs represent a maximum specific capacitance of 51 F g-1.In addition,the device also has a lot of advantages,such higher energy density(28.5 Wh kg-1)and power density(2780 W kg-1).At the same time,it also can continue to work under bending or compression states with almost constant performance.We design and report a combined approach to high performance device.Specifically,each component of the device is optimized.Firstly,a flexible free-standing alkali-treated carbon nanotube(CNT)film with large specific surface area(269.5 m2 g-1)and abundant channels is prepared by a one-step carbonization.This free-standing electrode avoids the use of non-conductive polymer binder and improves the conductivity of the electrode.The interconnected carbon nanotubes form a 3D conductive network that exhibits ultra light,flexible and bendable characteristics.To make the voltage window for carbon materials larger than 1 V,the most important thing is to inhibit or reduce the occurrence of hydrogen evolution reaction(HER)in a charging-discharging process.Due to a thermodynamic favourable process,sodium ions can be adsorbed on sp3 defect sites consisting of C or O,and the adsorption of sodium ions can effectively inhibit the adsorption of H+,thereby reducing the activity of HER.We can increase 0.4 V for the voltage window by modifying our CNT films.Secondly,we successfully synthesize amorphous electrode after growing MnO2 on CoMoO4 nanowires.The amorphous state of an electrode material can improve electrochemical performance and suppress damage during the charging and discharging process.In addition to the design of both positive and negative materials,we also use redox additive in 1 M Na2SO4 electrolyte to increase the capacitance of the whole device.Finally,A high energy density of 62.9 W h kg-1 at a power density of 984 W kg-1 is achieved for our aqueous hybrid supercapacitor(KF-CMNWs/NF//M-CNTF)with a high voltage window of 2.4 V.Meanwhile,the device has an excellent cycle performance(96.8%capacitance retention after 10,000 cycles).